Short sheet detector on coil stock shear



SHORT SHEET DETECTOR ON COIL STOCK SHEAR Filed July 19, 1962 4 Sheets-Sheet 1 INVENTOR JOSEPH 1. SEWE L DMIZMMVMZZ(MQW ATTORNEYS 4 Sheets-Sheet 2 JOSEPH J. SEHNELLO June 1964 J. J. SENNELLO SHORT SHEET DETECTOR ON con. STOCK SHEAR Filed July 19, 1962 June 23, 1964 J. J. SENNELLO 3,138,047

SHORT SHEET DETECTOR ON COIL STOCK SHEAR Filed July 19, 1962 4 Sheets-Sheet 3 I 35 I3 n "W 1'.

48 I08 27 as low JOSEPH J. SE NNELLO ATTORNEYS June 23, 1964 J. J. SENNELLO 3,138,047

SHORT SHEET DETECTOR ON COIL STOCK SHEAR Filed July 19, 1962 4 Sheets-Sheet 4 INVENTOR JosEPH J. SEHNELLO ATTORNEYS United States Patent 3,138,047 SHORT SHEET DETECTOR 0N COIL STOCK SHEAR Joseph J. Sennello, Oak Lawn, Ill., assignor to Continental Can Company, Inc., New York, N.Y., a corporation of New York Filed July 19, 1962, Ser. No. 210,967 12 Claims. (Cl. 83-406) This invention relates in general to new and useful improvements in attachments for shears, and more particularly relates to a novel short sheet detector for a shear adapted to continuously shear sheets from coil stock.

In the normal operation of a shear, stock is fed until the stock contacts a stop, after which the stock is sheared. Since the stop is accurately located with respect to the shear, the position of the stop and the speed of the feed rolls determines the maximum length of the sheared sheets. However, during high speed continuous shearing operations occasionally the stock will not be fed far enough due to a malfunction of the stock feed rolls or other conditions resulting in the leading edge of the stock being short of the stop. This causes the sheet being sheared to be shorter than normal in the amount that the stock was short of touching the stop at the time of shear- 111g.

In certain instances it is desired to have very accurately cut sheets. This is particularly true of the can-making industry. Therefore, in accordance with this invention, a detector is provided for indicating when a sheet is shorter than a predetermined minimum so that the operator of a shear will automatically be aware of the improper feeding of stock through the shear.

Another object of this invention is to provide a short sheet detector which is primarily intended for use on a flying shear of the type which has a sheet stop movable with the shear structure wherein a gauging of the length of sheets being cut may be had, the short sheet detector cooperating with the stop and being constructed to eliminate the passing on of sheets which are not of the required size.

Another object of this invention is to provide a novel short sheet detector intended for use on a shear which continuously cuts coil stock into sheets, the detector being connected to a gate in the sheet conveying system of the shear whereby when a shorter than acceptable sheet is formed, and as the sheet passes along conveying means extending from the shear, the sheet is automatically removed from the conveying means and collected with other short sheets.

Still another object of this invention is to provide a novel short sheet detector which operates in conjunction with a sheet stop; the short sheet detector including an apertured member, a sensing device underlying the aperture of the member, and a signal transmitting device overlying the aperture wherein when the aperture is not covered by a sheet, a signal will be directed to the sensing device to indicate the existence of a short sheet; the apertured member being adjustable relative to the sheet stop to provide a defininte limit within which sheets may be accepted.

A further object of this invention is to provide a short sheet detector which includes an apertured member closely positioned relative to a sheet stop surface, a signal device overlying the aperture of the member for directing a signal therethrough, a sensing device beneath the aperture for receiving the signal from the signal transmitter when a sheet fails to completely overlie the aperture, the sens ing device being part of a sensing circuit wherein when a signal is received by the sensing device at a proper time, the sensing circuit is so energized to efiect the energization of an associated detector device.

A still further object of this invention is to provide a novel short sheet detector which includes a detector circuit having incorporated therein an electrical bridge with two adjacent legs of the bridge having like sensing devices therein, an apertured member associated with a conven tional sheet stop with the aperture being accurately located relative to the sheet stop, a signal transmitter over lying the apertured member for directing a signal through the aperture, and one only of the sensing devices under-' lying the aperture whereby the resistance of the one sensing device is caused to be changed in the event a sheet is short and fails to completely cover the aperture, and there being provided a circuit controlling switch closeable at the time of the shearing of the stock whereby when the circuit of the bridge is completed, and the resistance of the one sensing device is changed, the bridge will be unbalanced and indicate a short sheet.

Yet another object of this invention is to provide a novel short sheet detector in accordance with the foregoing, wherein sheet movement control means are connected to the detector circuit for actuation, and the sheet movement control means includes a sheet movement control device disposed remote from the apertured member, and a memory device is coupled to the sheet control device for actuating the same intirned relation to the movement of a sheet thereby, whereby detected short sheets may be diverted from a sheet delivery conveyor.

With the above, and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a schematic sectional side elevation view of a sheet forming line wherein sheets are sheared from coil stock with the sheet forming line incorporating the short sheet detector of this invention.

FIGURE 2 is a plan view of the sheet forming line of FIGURE 1 and shows further the details thereof.

FIGURE 3 is an enlarged fragmentary vertical sectional view taken along the line 3-3 of FIGURE 2 and shows more specifically the details of the means for shearing a sheet and for detecting the existence of a short sheet.

FIGURE 4 is a fragmentary horizontal section view taken along the line 44 of FIGURE 3 and shows further the details of the short sheet detector.

FIGURE 5 is a fragmentary longitudinal sectional view showing the specific details of the sensing device of the short sheet detector and the apertured member in which the sensing device is mounted.

FIGURE 6 is an enlarged fragmentary transverse ver tical sectional view taken along the line 66 of FIGURE 3 and shows more specifically the details of a signal transmission device and the sensing device associated therewith.

FIGURE 7 is a fragmentary schematic perspective view showing the control gate for directing short sheets from the normal path of travel of sheets and shows a short sheet in position to be detected.

FIGURE 8 is a schematic view similar to FIGURE 7 and shows the short sheet of FIGURE 7 being directed from the sheet conveyors by the gate.

FIGURE 9 is a wiring diagram of the electrical circuit of the short sheet detector and shows the specific details thereof.

Referring now to the drawings in detail, it will be seen that there is illustrated in FIGURES l and 2 a shear line, generally referred to by the numeral 10, in which the invention is incorporated. The shear line 10 is schematically illustrated as including a coil holder 11 which supports a. coil of metal stock for unreeling, the coil generally being referred to by the numeral 12. The metal stock 13 of I the coil passes through a flying shear, generally referred to by the numeral 14, wherein the metal stock 13 is cut into individual sheets 15. After the sheets 15 pass out of the shear 14, the sheets 15 are disposed on a conveyor 16 and are then transferred to a conveyor- 17. Although only two conveyors 16 and 17 have been schematically illustrated, it is to be understood that any number of conveyors may be utilized and it is not necessary that the conveyors be of the delivery belt type illustrated in the drawings.

The shear line includes a receptacle 18 disposed at the discharge end of the conveyor 16 and a second receptacle 19 disposed at the discharge end of the conveyor 17. The receptacle 19 is intended to receive properly cut sheets whereas the receptacle 18 is intended to receive sheets which are cut too short and which have been detected and rejected in accordance with this invention. In order that short sheets may be directed into the receptacle 18, a gate 20 is disposed intermediate the conveyors 16 and 17. The gate 20 normally functions as a dead plate and is pivotal upwardly to the dotted line position thereof in FIGURE 1 so as to direct a sheet down into the receptable 18. The gate is automatically actuated by a short sheet detector, which is the subject of this invention, the short sheet detector being generally referred to by the numeral 21.

The shear 14 has only been illustrated to the extent that the general operation of the invention is understandable. Reference is accordingly made to the patents to Sarka, Patent No. 2,827,962, granted on March 25, 1958, and Canadian Patent No. 616,466, issued on March 14, 1961, which disclose flying shears which are formed in the same general manner as is the shear 14.

The shear 14 includes a suitable frame 22 which supports a pair of feed rolls 23 between which the metal stock 13 passes. After the metal stock passes between the feed rolls 23, it passes between a pair of platens 24 and 25 which carry dies 26 and 27, respectively. The platen 24 extends between and is fixedly supported by a pair of plates 28 which are mounted on a pair of eccentric shafts 29 and 30 for oscillatory movement relative to the frame 22. In this manner the platen 24 and the die 26 carried thereby have an oscillatory movement imparted thereto.

The platen 25 is slidably mounted in the plates 28 for movement therewith and has vertical reciprocatory movement relative thereto. Reciprocatory movement of the platen 25 is accomplished by means of connecting rods 31 carried by the eccentric shaft 30 so that as the plates 28 normally move downwardly, the platen 25 and the die 27 carried thereby move upwardly relative to the plates 28 so that for the most part the die 27 remains vertically stationary with respect to the frame 22 while the die 26 vertically reciprocates, and the dies 26 and 27 move back and forth along the direction of stock travel in unison. It is to be understood that at the time the die 26 cooperates with the die 27 to effect a shearing of the metal stock 13, the dies 26 and 27 are being moved by the plates 28 in the direction of movement of the metal stock 13 and at the same rate so that except for the shearing action on the dies 26 and 27, there is no relative movement between the metal stock 13 and the dies 26 and 27.

At this time it is pointed out that due to the horizontal movement of the plates 28, there is a slight vertical movement imparted to the platen 25 with respect to the line of movement of the metal stock 13. This vertical movement is in the form of a minute lowering of the platen 25 following the shearing operation and a later elevation of the platen 25 for a purpose to be described in detail and as is set forth in the Sarka patents.

As is best shown in FIGURES 1, 3 and 4, the platen 25 has a support member 32 secured thereto and a plurality of fingers 33 extend from the support member 32 in cantilever relation. The fingers 33 extend in the direction of stock travel from the support 32 and are for the purpose of supporting the metal stock as it is fed between the dies 26 and 27 by the feed rolls 23. In accordance with the conventional shearing practice, a sheet stop 34 is carried by fingers 33 for movement therewith. Since the fingers 33 not only move vertically, but also back and forth, it will be seen that the sheet stop 34, which has a sheet engaging face 35, is moving at the same rate as the metal stock 13 when the metal stock 13 approaches the face 35 of the stop 34 so that the leading edge of the metal stock 13 may engage the face 35 without undue impact. In the conventional operation of the shear 14, immediately upon the shearing of a sheet from the metal stock 13, the fingers 33 and the sheet stop 34 are lowered to the extent that the newly formed sheet 15 rests upon the conveyor 16 and is moved thereby over the sheet stop 34 and off of the fingers 33.

A pair of vertically downwardly resiliently urged stock clamping shoes 122 are mounted on brackets 123 which are attached to the plates 28 such as by welding. These shoes engage the metal stock 13 to assist in forwarding the stock against the sheet stop 34 and also aid in preventing the strip stock from buckling between the dies and the stop.

Although the sheet stop 34 provides for a maximum length of sheet being sheared by the shear 14, it does not provide an adequate control for the length of the sheets 15 being sheared from the metal stock 13. In the first place, the metal stock 13 cannot be overfed to constantly assure engagement of the leading edge of the metal stock with the face 35. Therefore, it is necessary that the feeding of the metal stock 13 be controlled so that the leading edges thereof only touch the face 35. This is virtually impossible to consistently do at the high feed rates of the present shears. On the other hand, in many instances, particularly in the can-making industry, it is necessary to have the length of the sheets accurately controlled to minimize waste. Since the further operations to be performed on a sheet utilize substantially all of the sheet, if a sheet is too short, then some of the can elements formed therefrom will be lacking material and will thus be defective. It is, therefore, the main purpose of the invention to detect sheets of abnormally short length and eliminate such sheets from subsequent fabrication operations for which the sheets are intended. Since any malfunction of the equipment will result in a sheet being cut shorter than normal and never longer than normal, it is not necessary to provide for the detection of abnormally long sheets.

Reference is now made to FIGURE 5 in particular wherein it will be seen that the sheet stop 34 has a cavity 36 therein in which there is mounted a member 37 for movement in the general direction of sheet and stock travel. The sheet stop 34 has an upper opening 38 disposed immediately in advance of the face 35 and opening downwardly into the cavity 36. The member 37 has a vertical opening 39 which terminates at its upper end in a horizontal opening 40, which, in turn, has a small vertical opening 41 which opens through the upper surface of the member 37 in alignment with the opening 38. The opening 41 is of a much smaller width than the opening 38 so that in all adjusted positions of the member 37, the opening 41 is aligned with the opening 38. At this time it is pointed out that a practical width of the opening 41 has been found to be 0.004 inch.

In order to provide for accurate accept tolerance control of the lengths of sheets 15 being sheared, accurate means are provided for positioning the member 37 relative to the sheet stop 34. The means for positioning the member 37 includes a shaft 42 which extends through a bore 43 in the sheet stop 34 and into the cavity 36. The inner end of the shaft 42 is threaded into an internally threaded bore 44 in one end of the member 37. The opposite end of the shaft 42 is provided with a control knob 45 having a dial portion 46 which accurately indicates the amount of movement of the member 37 and thus the amount of movement of the opening 41 and the relationship of the opening 41 to the face 35. A collar 47 carried by the shaft 42 and positioned in an enlargement 48 of the bore 43 cooperates with the control knob 45 to prevent axial shifting of the shaft 42. Before further describing structural details of apparatus of the short sheet detector 21, it is deemed advisable to make reference to the wiring diagram of FIGURE 9.

The short sheet detector 21 utilizes a signal transmitter and a receiver. It has been found that infrared rays provide very good signals and accordingly, in accordance with the invention, a signal transmitter of the infrared radiation type is provided, the signal transmitter being generally referred to by the numeral 50. The signal transmitter 50 is schematicalyl illustrated as including a power source 51 to which there is connected a resistance wire infra-red radiation source 52. Of course, if desired, a switch may be incorporated in the circuit.

The short sheet detector 21 also includes a detector circuit, generally referred to by the numeral 54. The detector circuit 54 includes a bridge 55 which includes terminals 56, 58 and 59. A wire 60 extends between the terminals 56 and 59 and has incorporated therein a sensing device 61 in the form of an infra-red sensitive cell. Another wire 62 extends from the terminal 56 to the terminal 58 and has incorporated therein a second sensing device 63 which is also an infra-red sensitive cell and which has the same characteristics as the sensing device 61. A wire 64 extends between the terminals 58 and 59 and has incorporated therein resistors 65 and 67 and a bridge balancing potentiometer 57.

A wire 68 extends between the terminal 56 and potentiometer 57 and has a battery 69 incorporated therein. The wire 68 also has a switch 70 incorporated therein so that the bridge 55 may be selectively energized. It is to be understood that the bridge 55 is prior balanced by means of the potentiometer 57 so that when no infra-red radiation is directly impinged on the sensing device 61, there is no out-put voltage across the terminals 58 and 59.

The detector circuit 54 also includes a coil 71 of a solenoid control switch 72. The coil 71 is part of a commutating network and has one end thereof attached to a Wire 73 which extends to an energizing battery 74. A resister 75 is incorporated in the wire 73. A wire 76 leads from the opposite terminal of the battery 74 and is connected to a biasing voltage source 77. A wire 78 is connected to the coil 71 at the end thereof remote from the wire 73 and the opposite end of the wire 78 is connected to the wire 76. A condenser 79 is incorporate in the wire 78. A wire 80 leads from the wire 78 between the condenser 79 and the connection of the wire 78 to the wire 76. The opposite end of the wire 80 is connected to the wire 73 intermediate the coil 71 and the resister 75. A condenser 81 is incorporated in the wire 80.

The detector circuit 54 also includes a thyratron 82. The thyratron 82 has a cathode 83 which is connected by means of a Wire 84 to the wire 76 adjacent the biasing voltage source 77. A wire 85 extends from the cathode 83 to a grid 86 of the thyratron. A wire 87 extends from the terminal 58 of the bridge 55 to a grid 88 of the thyratron 82. The thyratron 82 also includes a plate 89 to which there is connected a Wire 90. The opposite end of .the wire 90 is connected to the wire 78 intermediate the coil 71 and the condenser 79. A resister 91, is incorporated in the wire 90.

The switch 70 is normally open and is momentarily closed by means of a cam 92 which is coupled for operation in timed relation to the operation of the shear 14. It is to be understood that the switch 70 is momentarily closedat the time the dies 26 and 27 are substantially half way through'the actual shearing operation. When the switch 70 is closed, if there is no radiation from the source of radiation 52 acting on the sensing device 61, then the bridge 55 will remain in a balanced 'state and there will be no out-put voltage by the terminals 58 and 59. On the other hand, if there is radiation directed to the sensing device 61 from the infra-red radiation source 52, then there will be an unbalanced con dition in the bridge 55 and an out-put voltage between the terminals 58 and 59 will exist. The out-put voltage of the bridge at the terminals 58 and 59 'is impressed on the grid 88 of the thyratron 82 and if it is of sufiicient magnitude, will cause this tube to fire. The firing of the thyratron 82 causes a circuit to be completed from the plate 89 of the thyratron through the wire 90, the coil 71, the energizing battery 74 and the wires 76 and 84 to the cathode 83 of the thyratron 82. This will result in the momentary actuation of the switch 72 for a purpose to be described hereinafter.

It is to be understood that once the thyratron 82 is fired by the voltage impressed on the grid 88, it will con tinue to conduct even though the voltage on the grid 88 is reduced by the opening of the switch 70. In order to turn the thyratron off within a predetermined length of time after it has been fired, the commutating network is employed with the resistors 75 and 91 and the condensers 79 and 81 functioning to obtain this result in a conventional manner. It is to be understood that the thyratron tube 82 is adjusted by means of the biasing voltage source 77 in a manner that a predetermined voltage will have to be impressed on the grid 88 of the thyratron before the tube will fire. By means of the biasing voltage source adjustment, the sensitivity of the detector circuit can be varied so that the thyratron will be caused to fire when varying radiation is impressed on the sensing device 61. This has a definite advantage, as will be described hereinafter.

Reference is once again made to FIGURE 5, as well as FIGURE 6, of the drawings. In FIGURE 5 it will be seen that the sensing devices 61 and 63 are mounted within the member 37 in the recess 40 thereof with the sensing device 61 underlying the opening 41 for receiving radiation through the aligned openings 38 and 41. On the other hand, the sensing device 63 is completely protected at all times against radiation and does not sense radiation as does the sensing device 61.

The radiation source 52 is mounted in overlying relation to the opening 38 so that infra-red rays may be directed downwardly through the opening 38. As will be further explained later, the radiation source 52 is stationary with respect to the frame 22 and will be aligned with the opening 38 only at certain times during the gauging and shearing cycle; one of the times being when the leading edge of the metal stock 13 is approaching the stop face 35. Due to the fact that the opening 41 is aligned with the opening 38, it will be seen that portions of the infra-red rays are directed to the sensing device 61 through the opening 41. However, since the metal stock 13 is continuously fed, most of the time the infra-red rays, which are referred to by the numeral 93, are blocked by the previously cut sheet 15. Shortly after the previously cut sheet 15, which has not been illustrated in FIGURES 5 and 6, uncovers the openings 38 and 41, the leading edge of the metal stock 13 slides onto the sheet stop 34 and if a suflicient amount of metal stock 13 has been fed, the metal stock 13 will be overlying the opening 41 and prevent the rays 93 from being directed to the sensing device 61. Thus, when the switch 70 is automatically closed at the time of shearing, if sufiicient metal stock has been fed, no voltage will be directed tothe thyratron 82 from the bridge 55 to cause firing of the thyratron 82. on the other hand, if insufficient metal stock has been fed to cover the opening 41, then the infra-red rays 93 will pass through the opening 41 at the time of the closing of the switch 70 so as to impinge on the sensing device 61 and thus unbalance the bridge 55 to produce'a voltage for firing the thyratron tube 82. i

As was stated above, it has been found that a practical width of the opening 41 is 0.004 inch. .However, by adjusting the biasing voltage source 77, the opening 41, when only partially uncovered, can be effective to cause a sufiicient voltage out-put from the bridge 55 to cause firing of the thyratron 82. Thus, a closer gauging of the length of the sheets 15 than 0.004 inch can be obtained with the short sheet detector 21...

shear whereby said detector circuit is energized only in accordance with the length of a sheet at the time the sheet is being sheared 3. A short sheet detector for a shear comprising a sheet stop having a stop surface for determining a maximum sheet length, an apertured member having the aperture thereof positioned closely adjacent said stop surface for being covered by a sheet edge portion, a signal transmitter overlying the aperture, a sensing device underlying the aperture for receiving a signal through the aperture when a sheet is short, a detector circuit incorporating said sensing device, a control switch, means adapted to be coupled to the shear for closing said switch during the actual shearing of a sheet by the shear where by said detector circuit is effected only in accordance with the length of a sheet at the time the sheet is being sheared, and sheet movement control means coupled to said detector circuit for actuation thereby.

4. A short sheet detector for a shear comprising a sheet stop having a stop surface for determining a maximum sheet length, an apertured member having the aperture thereof positioned closely adjacent said stop surface for being covered by a sheet edge portion, a signal transmitter overlying the aperture, a sensing device underlying the aperture for receiving a signal through the aperture when a sheet is short, a detector circuit incorporating said sensing device, a control switch, means adapted to be coupled to the shear for closing said switch during the actual shearing of a sheet by the shear whereby said detector circuit is effected only in accordance with the length of a sheet at the time the sheet is being sheared, and sheet movement control means coupled to said detector circuit for actuation thereby, said sheet movement control means including a sheet movement control device disposed remote from said sheet stop and a memory device coupled to said sheet movement control device for actuating the same in timed relation to the movement of a sheet thereby.

5. The short sheet detector of claim 1 wherein said detector circuit includes a normally balanced electrical bridge, said sensing device being in one leg of said bridge and a second like sensing device being in an adjacent leg of said bridge, said second sensing device being mounted adjacent said first mentioned sensing device and protected from said signal transmitter.

6. The short sheet detector of claim 1 wherein said detector circuit includes a normally balanced electrical bridge, said sensing device being in one leg of said bridge and a second like sensing device being in an adjacent leg of said bridge, said second sensing device being mounted adjacent said first mentioned sensing device and protected from said signal transmitter, said bridge including a power supply, and said switch controlling said power supply.

7. The short sheet detector of claim 1 wherein said detector circuit includes a normally balanced electrical bridge, said sensing device being in one leg of said bridge and a second like sensing device being in an adjacent leg of said bridge, said second sensing device being mounted adjacent said first mentioned sensing device and protected from said signal transmitter, and means for constantly cleaning said sensing devices and said aperture.

8. The short sheet detector of claim 1 wherein said detector circuit includes a normally balanced electrical bridge, said sensing device being in one leg of said bridge and a second like sensing device being in an adjacent leg of said bridge, said second sensing device being mounted adjacent said first mentioned sensing device and protected from said signal transmitter, and means for constantly directing clear air over said sensing devices and through the aperture.

9. The short sheet detector of claim 1 wherein support means adjustably mount said apertured member for movement relative to said sheet stop to vary sheet length tolerance.

10. A short sheet detector in accordance with claim 1 wherein the sheet detector is particularly intended for use with flying shears of the type including sheet supporting fingers movable with the shears, and means mounting said sheet stop on said fingers for movement therewith.

11. The short sheet detector of claim 1 wherein said signal transmitting device is an infra-red radiation source and sensing device is an infra-red heat sensitive cell.

12. The short sheet detector of claim 1 together with support means adjustably mounting said sheet stop, said apertured member is supported by said sheet stop for movement therewith to vary over-all sheet length, and other support means adjustably mounting said apertured member for movement relative to said sheet stop to vary sheet length tolerance.

No references cited. 

1. A SHORT SHEET DETECTOR FOR A SHEAR COMPRISING A SHEET STOP HAVING A STOP SURFACE FOR DETERMINING A MAXIMUM SHEET LENGTH, AN APERTURED MEMBER HAVING THE APERTURE THEREOF POSITIONED CLOSELY ADJACENT SAID STOP SURFACE FOR BEING COVERED BY A SHEET EDGE PORTION, A SIGNAL TRANSMITTER OVERLYING THE APERTURE, A SENSING DEVICE UNDERLYING THE APERTURE FOR RECEIVING A SIGNAL THROUGH THE APERTURE WHEN A SHEET IS SHORT, A DETECTOR CIRCUIT INCORPORATING SAID SENSING DEVICE, A CONTROL SWITCH, AND MEANS ADAPTED TO BE COUPLED TO THE SHEAR FOR CLOSING SAID SWITCH DURING THE ACTUAL SHEARING OF A SHEET BY THE SHEAR WHEREBY SAID DETECTOR CIRCUIT IS EFFECTED ONLY IN ACCORDANCE WITH THE LENGTH OF A SHEET AT THE TIME THE SHEET IS BEING SHEARED. 